Insight into the Interfacial Process and Mechanism in Lithium–Sulfur Batteries: An In Situ AFM Study

Abstract

Lithium-sulfur (Li-S) batteries are highly appealing for large-scale energy storage. However, performance deterioration issues remain, which are highly related to interfacial properties. Herein, we present a direct visualization of the interfacial structure and dynamics of the Li-S discharge/charge processes at the nanoscale. In situ atomic force microscopy and ex situ spectroscopic methods directly distinguish the morphology and growth processes of insoluble products Li₂ S₂ and Li₂ S. The monitored interfacial dynamics show that Li₂ S₂ nanoparticle nuclei begin to grow at 2 V followed by a fast deposition of lamellar Li₂ S at 1.83 V on discharge. Upon charging, only Li₂ S depletes from the interface, leaving some Li₂ S₂ undissolved, which accumulates during cycling. The galvanostatic precipitation of Li₂ S₂ and/or Li₂ S is correlated to current rates and affects the specific capacity. These findings reveal a straightforward structure-reactivity correlation and performance fading mechanism in Li-S batteries.